The present invention relates to the field of optical fiber coupling technology. It relates to a positioning system for automatically positioning and attaching at least one optical fiber inserted into said positioning system along a predetermined optical axis 2, said positioning system comprising a base member with a flat upper surface and a V-shaped receiving channel which is parallel to said upper surface and is formed therein for receiving at least one optical fiber; said system also includes a separate spring-action retaining member which is arranged on the upper surface of the base member for securing the minimum of one optical fiber inserted into the receiving channel.
Such a positioning system is know, for example, from U.S. Pat. No. application No. 4,973,126 A.
With the increasing widespread use of optical fibers, which have become popular because of their high transmission capacity and their lack of sensitivity to interference fields, there has also been an increasing demand for connectors that make it possible to optically couple two optical fibers detachably and with the lowest possible attenuation or to connect an optical fiber to a transmission or receiving element. It is self-evident that a very high precision (less than 1 xcexcm) is necessary in positioning and coupling the fibers in optical coupling in order to obtain low values for insertion damping (e.g., less than 0.5 dB) and high values for reflux damping (e.g., g reater than 60 dB) because of the small diameter of the fibers (for example, fiber diameter 125 xcexcm) and because of the even smaller mode field diameter (for example, approx. 10 xcexcm with a monomode fiber). At the same time, the coupling device should be mechanically sturdy, reliable in functioning even with repeated connection operations, easy to handle and inexpensive to manufacture in large numbers.
Traditional connectors for optical fibers such as those available commercially by the present applicant under the brand name Optoclip ll use a precision mechanical centering element, whereby for positioning and centering the fibers to be inserted, said fibers are passed through the center of a group of three beads arranged in an equilateral triangle, thereby pre-centering them. A pair of closely spaced cylinders aligned parallel with one another and with the optical axis are provided in the interior of the element for precision centering and securing so that the two fiber ends to be coupled come to lie between the cylinders and are secured in position by spring-action balls sitting above them. Such a traditional connector is complicated to manufacture and assemble and is also relatively sensitive mechanically.
Therefore, there have already been various proposals for producing positioning and centering elements and systems for coupling optical fibers using the relatively new micromechanics based on silicon technology so that these elements would be relatively simple to manufacture by wellknown technologies, would be mechanically sturdy and would be characterized by a high precision. Various proposals use bodies made of a single-crystal silicon with a predetermined crystal orientation for receiving and supporting the optical fibers, where a V-shaped groove or channel running in the direction of the optical axis is produced in these monocrystalline bodies by wet chemical etching or by comparable processing operations. The ends of the optical fibers to be coupled are then inserted into or placed in this V-shaped receiving channel and are centered in the channel and secured there by a traditional mechanical device pressing on the body with a spring-action from above. A typical solution of this type is disclosed in the above-mentioned publication U.S. patent application Ser. No. 4,973,126 A, where a silicon plate mounted in a plastic block accommodates the two fiber ends in a V-groove. The spring-action pressing device here consists of a cover plate made of glass and a spring clip which is pushed over the entire arrangement at the side and presses the cover plate against the silicon plate. This known solution ha s the disadvantage in particular that it is not suitable for a connector, but instead must be carefully assembled from the various individual parts for each coupling operation. A comparable solution for coupling an optical fiber to an active optical element can be found, for example, in U.S. patent application Ser. No. 4,756,591 A or U.S. Pat. No. 4,802,727 A.
A more extensive micromechanical solution for a connector for optical fibers is known from U.S. patent application Ser. No. 5,377,289 A, where positioning devices produced entirely by micromechanical processing of silicon and each comprising two arms are used for centering and securing the inserted optical fibers. The arms are each provided with a V-groove and are arranged one above the other in such a way that the V-grooves are opposite one another and form a receiving channel for the fibers. At one end, the channel is conically enlarged by selective directional etching, thus facilitating insertion of the fibers. At the other end, the channel is tapered. At the same time, the arms there can also be bent outward, so that a fiber inserted into the channel causes the arms to bend outward while at the same time being clamped between the arms and centered there by means of the restoring forces. However, the complete connector consists of a plurality of small individual parts to be assembled in a precision manner, so that assembly is especially difficult and complicated.
Other solutions where spring-action tongues projecting over the groove at the side are used to secure the optical fibers in the V-groove of the Si receiving plate, said tongues being produced by applying a suitable layer to the surface of the silicon receiving plate and then etching it away selectively, are known from European Patent Application No. 805,994 A1, for example, or from the article by C. Strandman and Y. Backlund, xe2x80x9cBulk Silicon Holding Structures for Mounting of Optical Fibers in V-Grooves,xe2x80x9d J. of Micromechanical Systems, Vol. 6, No. 1, March 1997 pages 35-40. With these solutions, the tongues have a relatively great mechanical susceptibility to breakage. On the other hand, the entire device is produced in a continuous and very complicated sequence of process steps, which limits the yield and makes production complicated and expensive.
Therefore, the object of this invention is to create a positioning device for optical fibers that has a simple design and is easy to manufacture, easy to assemble, has a high precision, is mechanically sturdy and can be produced reliably and inexpensively by a micromechanical processing operation which involves a relatively small number of steps.
This object is achieved with a positioning device of the type mentioned in the preamble by the fact that the retaining member comprises a membrane which is elastically deflectable at a right angle and is arranged parallel to the upper side of the base member above the receiving channel and perpendicular to the upper side of the base member, said membrane being deflected when the minimum of one optical fiber is inserted into the receiving channel, and with its restoring force it secures the minimum of one optical fiber in the receiving channel. Using the membrane according to this invention yields a mechanically very stable and compact design of the device whose individual parts can be manufactured and assembled very easily. In particular, the membrane retaining member is suitable for production by micromechanical methods.
To facilitate insertion of the optical fibers into the receiving channel, according to a first preferred embodiment of the device according to this invention, a centering area which tapers from the outside to the inside toward the end of the receiving channel is provided in the base member on at least one end of the receiving channel, said centering area causing the proper alignment of the minimum of one optical fiber with the end of the receiving channel when the optical fiber is inserted into the positioning device.
The positioning device according to this invention can be used for coupling an optical fiber to an active optical element such as a laser diode or the like. However, this device can also be used in particular for coupling two optical fibers when they are inserted from two opposite directions into the positioning device according to a second preferred embodiment for positioning and securing optical fibers that abut against one another end to end, and the centering area is provided at both ends of the receiving channel.
Centering of the optical fibers inserted can be further improved if, according to another preferred embodiment, the centering area(s) of the base member is/are divided into a pre-centering area and a precision centering area arranged between the pre-centering area and the respective end of the receiving channel. The pre-centering area narrows the clearance for the inserted fiber end to the smaller area, while the actual centering with the inlet of the receiving channel is accomplished through the precision centering area.
The base member is preferably designed as a solid plate of a single-crystal material, in particular silicon, and the V-shaped receiving channel and optionally also the centering areas and pre-centering and precision centering areas within the base member are produced by micromechanical processing, especially by etching the channel in the solid plate. In this way, a sturdy and high-precision base member is made available by using standard methods.
If the positioning device according to this invention is provided for detachable insertion of optical fibers, it is advantageous because of the mechanical burden due to the inserted fiber ends if, according to another embodiment, at least the V-shaped receiving channel plus optionally the centering areas and pre-centering areas and precision centering area are protected from mechanical stress by a wear layer, especially SiO2.
Another preferred embodiment of the positioning device according to this invention is characterized in that the membrane is arranged on the lower side of the retaining member, the membrane has at least one passage through it and a trough-shaped recess is provided above the membrane in the retaining member to receive an index matching fluid. A supply of index matching fluid can be kept on hand in the trough-shaped recess so that the fluid surrounds the ends of the optical fibers beneath the membrane through the passage in the membrane. If the fibers are inserted and removed repeatedly, which is the usual practice with a connector, the resulting loss of index matching fluid can be replenished from the reservoir in the trough-shaped recess. This greatly prolongs the service life of such a plug connector.
The retaining member is preferably designed as a solid plate of a monocrystalline material, especially silicon, and the membrane is produced from the solid plate by micromechanical processing, especially by etching within the retaining member. In particular, the retaining member is made of silicon with a (100) orientation, with a centering area for centering the optical fibers on insertion being provided upstream and/or downstream from the membrane in the direction of the optical axis in the retaining member, and the centering areas of the retaining member are each bordered at the side by walls in the [111] crystal plane that had been etched in a selective manner as to direction. The lower side of the membrane and the centering areas are also preferably protected from mechanical stress by a wear layer, especially made of SiO2.
The connector according to this invention for detachably connecting two optical fibers is characterized in that it comprises a positioning system according to this invention for positioning and securing the two optical fibers.
A preferred embodiment of the connector according to this invention is characterized in that the connector comprises a housing with a device for assembly of the positioning system; the assembly device has a perpendicular assembly shaft into which the positioning system is inserted and held by means of an assembly member; said assembly shaft is bordered in the direction of the optical axis by transverse walls having insertion bores; the optical fibers to be joined can be inserted into the assembly shaft or the positioning system at the side through said insertion bores; the assembly shaft is bordered at the lower end by a V-shaped shaft bottom running parallel to the optical axis; the positioning device is inserted into the assembly shaft with the base member facing down, and the positioning device is centered in the assembly shaft by beveled edges adapted to the V-shaped bottom of the shaft on the lower side of the base member. Assembly and centering are facilitated by the assembly shaft, and the positioning device is protected by the assembly shaft. At the same time this yields a largely closed space.
Sealing this space for an index matching fluid is a achieved in particular by the fact that a trough-shaped recess to accommodate an index matching fluid is provided in the positioning device above the membrane in the retaining member, and a gasket, especially in the form of an O-ring, is arranged between the assembly element and the retaining member, surrounding the trough-shaped recess and sealing it at the top.
Additional embodiments are derived from the dependent claims.